In mobile communication systems, there is an increasing demand for a high-frequency signal processing integrated circuit which is directed to time division duplex (TDD) systems, such as wireless LAN, Bluetooth (trademark), and PHS (Personal Handyphone System), which perform reception and transmission of radio signals in separated time zones.
The above-mentioned mobile communication systems are required to realize reductions in spaces and costs of integrated circuits because miniaturization and cost reduction of mobile communication devices enhance popularization and convenience of the communication systems.
Currently, a front-end one-chip integrated circuit for processing communication signals from RF frequency to baseband frequency is realized. FIG. 11 shows the construction of a high-frequency amplifier for amplifying transmission and reception signals, which is included in the conventional integrated circuit.
With reference to FIG. 11, a high-frequency amplifier 1101 includes a low-noise amplifier 1102 and a power amplifier 1103. The low-noise amplifier 1102 amplifies a reception signal. The power amplifier 1103 amplifies a transmission signal. Transistors 1104 and 1105 are provided in the low-noise amplifier 1102 and the power amplifier 1103, respectively. Spiral inductors 1106 and 1107 are provided in the low-noise amplifier 1102 and the power amplifier 1103, respectively.
The transistors 1104 and 1105 are supplied with a DC power supply VDD through the spiral inductors 1106 and 1107, respectively.
A gate of the transistor 1104 is connected to a reception signal input terminal INRX and to an end of a resistor R1. Another end of the resistor R1 is connected to a common terminal of a transmission/reception selector switch SW1. One of two terminals of the switch SW1 is connected to ground that is shown by “∇” in FIG. 11, while the other terminal is connected to a positive side power supply terminal of a DC power supply Vbias1. A gate of the transistor 1105 is connected to a transmission signal input terminal INTX and to an end of a resistor R2. Another end of the resistor R2 is connected to a common terminal of a transmission/reception selector switch SW2. One of two terminals of the switch SW2 is connected to ground that is shown by “∇” in FIG. 11, while the other terminal is connected to a positive side power supply terminal of a DC power supply Vbias2.
Negative side power supply terminals of the DC power supplies Vbias1 and Vbias2 are connected to the ground. Further, sources of the transistors 1104 and 1105 are connected to the ground.
Next, a description will be given of the fundamental operation of the high-frequency amplifier 1101 in the reception mode and the transmission mode.
During the reception mode, a transmission/reception switching signal is input to a transmission/reception switching control terminal S1 and to a transmission/reception switching control terminal S2. At this time, the transmission/reception selector switch SW1 is connected to the terminal on the DC power supply Vbias1 side, and thereby the low-noise amplifier 1102 turns on. On the other hand, the transmission/reception selector switch SW2 is connected to the terminal on the ground side, and thereby the power amplifier 1103 turns off. The turned-on low-noise amplifier 1102 amplifies the reception signal inputted to the reception signal input terminal INRX, and outputs the signal to an output terminal OUTRX.
Further, during the transmission mode, the transmission/reception switching signal is input to the transmission/reception switching control terminal S1 and to the transmission/reception switching control terminal S2. At this time, the transmission/reception selector switch SW1 is connected to the ground terminal, and thereby the low-noise amplifier 1102 turns off. On the other hand, the transmission/reception selector switch SW2 is connected to the DC power supply Vbias2, and thereby the power amplifier 1103 turns on. The turned-on power amplifier 1103 amplifies the transmission signal inputted to the transmission signal input terminal INTX, and outputs the signal to an output terminal OUTTX.
In the conventional high-frequency amplifier, the spiral inductors fabricated in the integrated circuit are used as loads of the low-noise amplifier and the power amplifier, respectively (for example, refer to Patent Documents 1 and 2).
The reason is as follows. If the inductors are disposed outside the integrated circuit, inductances of bonding wires and board wirings are parasitic on the inductors, and capacitances of ESD (electro-static discharge) protection elements and pads are parasitic on the inductors, and consequently, it becomes difficult to oscillate the loads of the amplifiers at desired frequencies.
Patent Document 1: Japanese Published Patent Application No. Hei. 10-126174 (Page 20, FIG. 14)
Patent Document 2: Japanese Unexamined Patent Publication No. 2004-516737 (Page 10, FIG. 1)